Experimental Studies On Seismic Performance Of The Spandrel Column With Concrete Hooping Strengthening

Reinforced concrete deck arch bridge is widely used in Southwest China due to its reasonable force,convenient construction and low cost.Because of the constraints of historical economic conditions,a large number of existing reinforced spandrel column have generally lower reinforcement ratios,and the hoop reinforcement has weaker lateral hoop effect.In addition,the strength of concrete is relatively low,and the size of components is relatively small,and earthquake resistance is usually not considered.The design requirements make the anti-seismic capacity of the spandrel columns insufficient,and severe damage may occur under strong earthquakes.The method to strengthen spandrel column by enclosed reinforced concrete is widely used in columns because of advantages of improving significantly bearing capacity and easy construction,short construction period and economic benefits,but the research works are very less on strengthened reinforced spandrel column.To the above situation,the specialized theoretical and experimental research works have been carried out on the seismic performance of reinforced concrete spandrel columns and the hoop reinforcement spandrel columns.Conclusions are as follows:(1)Based on the investigation of seismic damage of typical reinforced concrete arch bridges,the characteristics of seismic damage caused by reinforced concrete deck arch bridges are analyzed,and the causes and mechanisms of seismic damage of this type of bridges are summarized,which can provide some reference value for seismic design of this type of bridges and seismic reinforcement and maintenance of old bridges.(2)Choosing the typical concrete-supported arch bridges for earthquake damage,a nonlinear calculation model was established,and the seismic performance evaluation of reinforced concrete spandrel columns was performed based on IDA.The analysis shows that the seismic performance of the long spandrel columns and short spandrel columns differs significantly.The seismic performance of the long spandrel columns is relatively poor,and the long spandrel columns are vulnerable components.The use of a hoop reinforced arched post improves the seismic performance of the post-reinforcement column,significantly reducing vulnerability and significantly improving ductility.It is suggested that in the seismic design of the upright column,the key parts of the long spandrel columns can be engraved with stirrups and additional main reinforcements to improve its seismic performance.(3)Taking the reinforced concrete arch upper column of the long-span up-concrete concrete arch bridge as the prototype,the low-cycle repeated load test of the scale-reducing reinforced concrete column model to simulate the earthquake is carried out.The effects ofshear span ratio,hoop ratio and reinforcement ratio parameters on the seismic behavior of the column were studied,and the failure mechanism,strength characteristics and deformation behavior of the column were revealed.The OpenSees fiber unit model is used to analyze the hysteretic behavior and damage process of the column,and the theoretical calculation is verified.The results show that the reinforced concrete arch upper column designed in China has poor ductility and energy dissipation capacity due to its special structural characteristics and mechanical characteristics.It is necessary to carry out seismic strengthening to improve seismic performance.Under the combined force of compression,bending and shearing,the arch-column model undergoes shear failure and bending failure with the increase of the shear-to-span ratio.The horizontal bearing capacity is gradually reduced,and the ductility and energy dissipation capacity are gradually enhanced.With the increase of the hoop ratio and the reinforcement ratio,the horizontal bearing capacity of the reinforced concrete arch upper column is gradually increased,and the ductility performance and energy consumption capacity are gradually enhanced.The nonlinear finite element analysis of the arched column and the reinforced truss column was carried out by using the OpenSees nonlinear software based on the fiber model.The numerical simulation was carried out to analyze the bearing capacity and seismic performance of the component.(4)Quasi-static test of the column model with the scale of 1:2 for ferrule reinforcement:comparative study on the seismic performance indexes of the failure characteristics,hysteresis curve,skeleton curve and cumulative hysteretic energy of the arched column model after reinforcement;Analyze the effectiveness of ferrule reinforcement on the seismic performance improvement of reinforced concrete arch columns.The test results show that with the increase of the thickness and reinforcement height of the ferrule reinforcement layer,the horizontal bearing capacity of the reinforced column is gradually increased,and the energy consumption capacity is gradually increased,but the increase of ductility is limited.(5)The damage mechanism of reinforced concrete piers under earthquake action is analyzed systematically.Based on the Park-Ang two-parameter damage model with effective energy consumption correction,combined with the reinforced concrete column seismic analysis database analysis of ferrules,the ferrule reinforcement column structure is proposed.Earthquake damage model.(6)Based on the analysis and summary of the factors affecting the shear strength of the ferrule-reinforced piers,the calculation of the shear capacity of the ferrule-reinforced piers based on the truss-arch model theory is carried out,and the shear coefficient of the ferrule layer is derived.The calculation formula of shear capacity is used,and the validity of theformula is verified by experimental data.